Hard-Coat vs. Soft-Coat Low-E: What's the Difference?

Low-E coatings come in two types with different manufacturing processes and performance characteristics. According to Lawrence Berkeley National Laboratory, understanding the difference helps you choose the right windows.

Hard-Coat (Pyrolytic) Low-E

According to FGIA, hard-coat Low-E is applied to hot glass during manufacturing:

How it's made: Metallic oxides are fused to glass at 1,200°F during float glass production.

Characteristics:

• Durable enough for single-pane use
• Moderate performance (emissivity ~0.15-0.20)
• Higher visible light transmission
• Can be used in any glass position

Best for:

• Single-pane applications
• Temperable glass
• Situations requiring durability

Soft-Coat (Sputtered) Low-E

According to LBNL, soft-coat Low-E is applied in a vacuum chamber after glass manufacturing:

How it's made: Multiple layers (often including silver) are deposited via magnetic sputtering in a vacuum.

Characteristics:

• Superior performance (emissivity ~0.04)
• Must be sealed inside insulated glass unit
• Can be optimized for different climates
• Multiple layer options available

Best for:

• Insulated glass units (IGUs)
• Maximum energy performance
• Climate-specific optimization

Performance Comparison

According to LBNL testing:

| Coating Type | Emissivity | Best U-Factor Achieved |
|--------------|------------|------------------------|
| Hard-coat | 0.15-0.20 | ~0.35 |
| Soft-coat | 0.04-0.10 | ~0.25 |
| Triple soft-coat | 0.02-0.04 | ~0.15 |

What Most Windows Use

According to GANA, approximately 90% of residential Low-E windows today use soft-coat technology. The superior performance and lower cost (in insulated units) have made it the standard.

Hard-coat is mainly used for specialty applications requiring single-pane Low-E or temperable Low-E glass.

The Bottom Line

For most residential window replacements, soft-coat Low-E is the standard—and provides the best performance. Hard-coat serves specialty needs but isn't typically what you'll find in replacement windows.

*For complete Low-E guidance, see: [Low-E Glass Coatings](/guides/low-e-glass-coatings)*